Magnetic material



May 15, 1928.

1,669,648 A. F. BANDUR MAGNETIC MATERIAL Filed Jan. 5, 192'? mmmfa/Adaflffiawda/ mz'.

tailed description of one embodiment t Patented May 15, 1928.

UNITED STATES PATENT orrica.

ADOLZH FRANCIS BANDUR, 0F BERWYN, ILLINOIS, ASSIGNOR TO. WESTERNELECTRIC COHRANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEWYORK.

HAGNETIC MATERIAL.

Application filed January 3, 1927. Serial No. 158,801.

This invention relates to magnetic materials and magnet cores, and moreespecially to magnet cores for loading coils for telephone circuits, andtheir method of production.

The principal object of the invention is the production of a magneticelement having low losses and a relatively high permeability to enable agiven inductance to be obtained from a minimum amount of material andpossessing to a high degree those electrical and magneticcharacteristics wh ch make it highly desirable in electrical signalingapparatus, particularly in loading coils for telephone circuits.

In accordance with one embodiment, the present invention contemplatesthe c0nstr uction of magnet cores of an alloy including nickel and ironin finely divided form combined with a suitable insulating material andheat treated to have ahigher inherent magnetic permeability and lowerinherent hysteresis loss than iron. More especlally, the inventioncontemplates the formation of the magnet cores of a nickel iron alloy infinely divided form in which the proportions of its constituents aremore than 25% of nickel and the remainder principall iron, and in a formwhich has proven satis actory the nickel content being approxlmately 78of the whole. The metal particles are cleaned and are then treated so asto chemically change the surface layer of each dust particle to. form anadhering coating thereon, after which the particles may be pressed intorings or cores of the desired shape and size. Or the chemically treatedparticles may be thoroughly mixed with a heat resistant material untilthey have received a secondary insulating coating before they arepressed into rings. The cores so formed are finally heat treated to theopti mum temperature for the particular combination of alloy andinsulator of which the cores are constructed'to give them the dc siredcharacteristics for the use to which they are to be put.

It is believed that the invention will be clearly understood from thefollowingI deereof and from the accompanying drawing, in Which Fig- .1is a p p tive view at a .sectlon of core but is adapted to theproduction of 4 cores of magnetic particles of many forms.

In carrying out the present invention the magnetic material is preparedin the follow 111g manner: The magnetic material employed is preferablyprepared from a nickel iron alloy commonly referred to as permalloywhich is treated in a manner more fully described in the copendinapplication of C. P. Beath and H. M. E Heinicke, Serial No. 101,179,filed April 10, 1926, to reduce the alloy to a finely divided form. Expename has proven that where low edd current losses are desired it isessential that the particles be of small size and preferably of suchsize that all of the particles will readily pass through what isgenerally known as a'120 mesh screen and a large percentage pass througha 200 mesh screen. According to one embodiment of the invention, thealloy is prepared by melting approximately 78% parts of nickel and 21parts of iron in an oxidizing atmosphere and pouring the resulting alloyinto a mold. hen prepared according to the foregoing process, theresulting alloy will be exceedingly brittle and is thereforeparticularly adapted to be reduced to a finely divided or dust form fromwhich the finished cores are molded. After the brittle ingots areobtained they are passed successively while hot throu h progressivelyreducing rolls which form t e alloy into flat slabs approximatelyonequarter of an inch thick. By the hot rolling' process the size of thecrystalline structure is materially reduced, which, since thedisintegration of the material takes place mainly at the crystalboundaries, is essential in order to have a satisfactory yield of dust.The rolled slabs are broken into short pieces and are then crushed in ajaw crusher, hammer mill, or any other suitable type of ap paratus inwhich a further reduction occurs. The material after being passedthrough the jaw crusher is ,subsequeutly rolled in a ball mill until itis reduced to a fine dust. The dust is sieved through a 120 mesh sieveand any residue is remelted and the foregoing operationis repeated toagain reduce the material to a finely divided form. Prior to theaddition of the insulating material, the finely divided particles of thenickel iron alloy are annealed in a proximately closed container at atemperature of ap- 750 C. to 980 6., the temper-' ature of about 925 C.having provcn to be one which produces very satisfactory results. It isthen necessary to again reduce the annealed alloy which is now in theform of a cake to a finely divided form, after which the particles arecleaned in any suitable manner, such as by immersing them in an acidsolution, to remove any grease or other adherent material so that achemical change may be readily eifected in the surface layers of theindividual particles.

'According to'one embodiment of the nvention, the surface layer of eachof the individual particles is chemically changed by combining theconstituents of the alloy present in the layer with sufficient oxygen toform an oxide, coating around each particle. This combination may beeffected in any one of several ways, a very satisfactory methodcomprising spreading the partlcles in a thin layer upon a suitable plateand heating the particles in the open air at a temperature ofapproximately 550 to 800 C. for about twenty minutes, by which treatmentan adherent, insulating coating consisting of oxides of nickel and ironis produced upon each of the particles. The oxidized particles may thenbe pressed into cores or rings-under high pressure Instead 'of formingthe cores or rings from the oxidized particles alone, satisfactory ringsmay be formed of the oxidized,

particles coated with a secondary insulating material. In order to formthis secondary coating, the oxidized particles are placed in a revolvingdrum and a heat resistant material, such as kaolin, whose insulatingproperties are unimpaired by high temperatures, 15

added, the amount of heat resistant material used depending upon thecharacteristics desired in the finished core. This mixture is tumbled inthe drum to thoroughly mix the ingredients until the dust particlesassume a uniform color which indicates that they are thoroughly coatedwith the secondary insulator. The insulated dust particles are then in aform suitable for pressing into cores or rings which are preferablyformed with a pressure of approximately 200,000 pounds per square inch.A high pressure is used in forming the rings in order to increase theirdensity,.since' it has been found that the permeability of the ringsincreases with increased density. Finally the cores, whether formed ofthe oxidized particles alone or of the'coated, oxidized particles,

are transferred to an annealing furnace Where they are annealed'at atemperature of from 425 C. to 780 C. A few test rings may be made ofdust insulated in the above manner and their permeability measured.Should their permeability be too low, it may be increased by theaddition of a predetermined amount of'nninsulated dust or dust which hasa light coating of insulator, to the insulated dust before it is pressedinto rings.

A plurality of rings thus formed are stacked coaxially to form a core onwhich the usual toroidal winding is applied, the number of such ringsused depending upon the existing electrical characteristics of thetelephone circuit with which the loading coils are to be associated.

Although in the above described method of treating the permalloyparticles they are t given a primary insulating coating by oxidizing'thesurfaceelayers of the individual particles by heating the particles inthe open air, it is, of course, to be understood that the primaryinsulating coating may be produced by effecting any chemical change inthe surface layer which will produce an insulating T coating upon theparticles. Instead of oxidizing the particles by heating them in air itis possible to effect an oxidation by heating the particles in pureoxygen or by treating the particles with an oxidizing agent. Or insteadof oxidizing the particles they may be treated with fluorine, bromine,chlo- 1 will retain their insulating properties during the subsequentheat treating operation, maybe employed to form a secondary insulatingcoating around the particles, and the resulting cores will besatisfactory from both a magnetic and electrical standpoint.

By using an alloy of the proportions stated in the preceding paragraphsand by following the foregoing method of insulating the individual alloyparticles and compressing the particles ,into cores or rings, magnetcores or rings are produced which have ex- .tremely desirable electricalcharacteristics with a minimum amount of materialemployed. By the use ofsuch cores or rings, inductance units having a higher premeability withequal or less hysteresis and eddy current losses as coresconstructedaccording to previously known methods, but with much lesscore volume and much less coil volume, are available.

What is claimed is:

. 1. As a new article of manufacture, a

magnetic substance composed of particles of a magnetic alloy, and aninsulating material consisting of the constituents of the alloychemically combined with another substance separating the particles.

2. As a new article of manufacture, a

- magnetic substance composed of finely divided particles of a nickeliron alloy, and an insulating material consisting of oxides of nickeland iron enveloping the particles.

3. As a new article of manufacture, a magnetic substance composed offinely divided particles of a magnetic alloy composed of more than 25%nickel and the remainder principally iron, and an insulating materialconsisting of oxides of the constituents of the alloy.

4. As a new article of manufacture, a magnetic substance composed ofparticles of a magnetic alloy, and a plurality of coatings of differentinsulating materials enveloping the particles, one of the coatingscomprising oxides of the constituents of the allo 5. As a new article ofmanufacture, a magnetic substance composed of particles of a magneticalloy, and a plurality of coatings of different insulating materialsenveloping the particles, one of the coatings obtained from the magneticalloy by chemical reaction and another coating comprising a heatresistant material.

6. As a new article of manufacture, a magnetic substance composed ofparticles of a magnetic alloy, a rimary coating obtained by the chemicalunion of the alloy with another material, and a secondary insulatingcoating of kaolin separating the particles.

7. As a new article of manufacture, a magnetic substance composed of amagnetic allow composed of more than 25% nickel and the remainderprincipally iron, a primary coating obtained by the chemical union ofthe constituents of the surface layer of each of the alloy particleswith oxygen, and a secondary insulating coating of kaolin separating theparticles.

8. The method of making magnetic structures composed of a magneticalloy, which consists in reducing the alloy to finely divided particles,heating the particles, again reducing the product so obtained to finelydivided particles, effecting a chemical change in the surface layer ofeach of the particles, forming a mass of such particles into ahomogeneous solid, and heating the solid mass to a high temperature.

9. The method of making magnetic structures, which consists in formingan oxide coating upon particles of a metallic alloy,

enveloping the oxidized particles with a heat resistant insulatingmaterial, and forming a mass of such insulated particles into ahomogeneous solid.

10. The method of making magnetic structures, which consists in treatingfinely divided particles of a magnetic alloy so as to effect a chemicalchange in the surface layer of each of the particles, enveloping thetreated particles with a heat resistant insulating material, and forminga mass of such insulated particles into a homogeneous solid.

11. The method of making magnetic structures, which consists in treatingparticles of magnetic material to effect a change in the surface layerof the particles, forming a mass of the changed particles into ahomogeneous solid, and heat treating the solid mass at a temperature toimpart thereto the desired magnetic properties.

12. As a new article of manufacture, a magnetic substance composed of amagnetic alloy, a primary coating obtained by the chemical union of thealloy with another material, and a refractory insulating materialseparating the particles.

13. A metallic structure comprisin elements of magnetic materialseparated y an insulating coating thereon comprising an oxide of saidmaterial and a non-conducting oxide of another material.

14. A magnetic structure comprising magnctic material in the form ofdust and an insulating coating on the dust particles comprising an oxideof said material and a nonconducting oxide of another material.

In witness whereof, I hereunto subscribe my name this 24th day ofDecember, A. D. 1926.

ADOLPH FRANCIS BANDUR,

